BackgroundToll-like receptor (TLR)-2/TLR1 heterodimers recognize bacterial lipopeptides and initiate the production of inflammatory mediators. Adaptors and co-receptors that mediate this process, as well as the mechanisms by which these adaptors and co-receptors function, are still being discovered.Methodology/Principal FindingsUsing shRNA, blocking antibodies, and fluorescent microscopy, we show that U937 macrophage responses to the TLR2/1 ligand, Pam3CSK4, are dependent upon an integrin, α3β1. The mechanism for integrin α3β1 involvement in TLR2/1 signaling is through its role in endocytosis of lipopeptides. Using inhibitors of endosomal acidification/maturation and physical tethering of the ligand, we show that the endocytosis of Pam3CSK4 is necessary for the complete TLR2/1-mediated pro-inflammatory cytokine response. We also show that TLR2/1 signaling from the endosome results in the induction of different inflammatory mediators than TLR2/1 signaling from the plasma membrane.Conclusion/SignificanceHere we identify integrin α3β1 as a novel regulator for the recognition of bacterial lipopeptides. We demonstrate that induction of a specific subset of cytokines is dependent upon integrin α3β1-mediated endocytosis of the ligand. In addition, we address an ongoing controversy regarding endosomal recognition of bacterial lipopeptides by demonstrating that TLR2/1 signals from within endosomal compartments as well as the plasma membrane, and that downstream responses may differ depending upon receptor localization. We propose that the regulation of endosomal TLR2/1 signaling by integrin α3β1 serves as a mechanism for modulating inflammatory responses.

The internalization of Borrelia burgdorferi, the causative agent of Lyme disease, by phagocytes is essential for an effective activation of the immune response to this pathogen. The intracellular, cytosolic receptor Nod2 has been shown to play varying roles in either enhancing or attenuating inflammation in response to different infectious agents. We examined the role of Nod2 in responses to B. burgdorferi. In vitro stimulation of Nod2 deficient bone marrow derived macrophages (BMDM) resulted in decreased induction of multiple cytokines, interferons and interferon regulated genes compared with wild-type cells. However, B. burgdorferi infection of Nod2 deficient mice resulted in increased rather than decreased arthritis and carditis compared to control mice. We explored multiple potential mechanisms for the paradoxical response in in vivo versus in vitro systems and found that prolonged stimulation with a Nod2 ligand, muramyl dipeptide (MDP), resulted in tolerance to stimulation by B. burgdorferi. This tolerance was lost with stimulation of Nod2 deficient cells that cannot respond to MDP. Cytokine patterns in the tolerance model closely paralleled cytokine profiles in infected Nod2 deficient mice. We propose a model where Nod2 has an enhancing role in activating inflammation in early infection, but moderates inflammation after prolonged exposure to the organism through induction of tolerance.

To date, there has been a lack of pediatric experience regarding the efficacy and tolerability of immune checkpoint inhibitors after haploidentical hematopoietic stem cell transplant (HSCT). We present the case of a 22-year-old female with multiple-relapsed Hodgkin lymphoma (HL) who presented with a new relapse after haploidentical (post-haplo) HSCT. Anti-PD-1 therapy with nivolumab resulted in significant objective disease response and clinical improvement without notable side effects, including the absence of a graft-versus-host disease (GVHD). This case report suggests that immune checkpoint inhibition may be safely tolerated even in the setting of haploidentical HSCT, without triggering overt GVHD.

Borrelia burgdorferi stimulates a strong inflammatory response during infection of a mammalian host. To understand the mechanisms of immune regulation employed by the host to control this inflammatory response, we focused our studies on adrenomedullin, a peptide produced in response to bacterial stimuli that exhibits antimicrobial activity and regulates inflammatory responses by modulating the expression of inflammatory cytokines. Specifically, we investigated the effect of B. burgdorferi on the expression of adrenomedullin as well as the ability of adrenomedullin to dampen host inflammatory responses to the spirochete. The concentration of adrenomedullin in the synovial fluid of untreated Lyme arthritis patients was elevated compared with that in control osteoarthritis patient samples. In addition, coculture with B. burgdorferi significantly increased the expression of adrenomedullin in RAW264.7 macrophages through MyD88-, phosphatidylinositol 3-kinase (PI3-K)-, and p38-dependent signaling cascades. Furthermore, the addition of exogenous adrenomedullin to B. burgdorferi-stimulated RAW264.7 macrophages resulted in a significant decrease in the induction of proinflammatory cytokines. Taken together, these results suggest that B. burgdorferi increases the production of adrenomedullin, which in turn negatively regulates the B. burgdorferi-stimulated inflammatory response.Borrelia burgdorferi is the causative agent of Lyme disease, the most common vector-borne disease in the United States. During infection of a mammalian host, B. burgdorferi disseminates from the site of entry to colonize distal tissues throughout the body, including the nervous system, heart, and joints. In each of these sites, the interaction of B. burgdorferi with the host results in the induction of an inflammatory response. This inflammatory response is important for the control and clearance of the infection, but if left unchecked, inflammation damages the host tissue and causes the clinical manifestations of Lyme disease, including neuroborreliosis, carditis, or arthritis. To avoid an overexuberant and potentially damaging inflammatory response, host cells employ multiple mechanisms for controlling inflammation.Adrenomedullin is a host factor that negatively regulates inflammation. It is expressed by numerous cells as a preproadrenomedullin peptide, which is further processed to yield two mature and active peptides, proadrenomedullin N-terminal 20 peptide (PAMP) and the 52-amino-acid adrenomedullin (34). Adrenomedullin is constitutively secreted from cells in its immature form (26, 51) and is activated after secretion by amidation of its C terminus (33).Adrenomedullin expression is induced by several bacterial pathogens (3,30,57) and by inflammatory environments (22,23,36,53). Adrenomedullin possesses immunomodulatory activities which have been demonstrated to downregulate inflammatory processes in a variety of different models, including models of arthritis. For example, the administration of exogenous adrenomedullin protects mice from arthr...

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